Sawin Lab

Our Research

We are interested in two general areas related to cellular organisation. Our current main interest is the regulation of cell polarity, under both normal and stress conditions; we also continue to study the molecular mechanisms underlying nucleation of the microtubule cytoskeleton. In both areas we use fission yeast Schizosaccharomyces pombe as a model single-celled eukaryote. We combine classical and molecular genetic analysis with live-cell fluorescence microscopy, biochemistry, proteomics/phosphoproteomics, and structural biology methods.

Cell polarity in fission yeast is regulated by multiple internal cues that cooperate and compete with each other. The Rho-family GTPase Cdc42 and its associated regulators and effectors control the actin cytoskeleton and exocytosis. Microtubules provide an additional level of control, through the microtubule-associated protein Tea1 and its interactors. We have shown how the Tea1/microtubule system coordinates polarity regulation by a conventional Cdc42 guanine-nucleotide exchange factor, Scd1, with regulation by an unconventional exchange factor, Gef1. Our work has also led to the discovery of new cell-polarity regulators outside of the Cdc42- and Tea1/microtubule-based systems, and a new understanding of how the conserved NDR kinase Orb6 regulates cell polarity. A major current focus is on how the stress-activated kinase Sty1 (homolog of human p38 MAP kinase) regulates cell polarity; we are addressing this through large-scale phosphoproteomics and genetics/biochemistry/microscopy approaches.

Microtubule nucleation in all eukaryotic cells depends on the γ-tubulin complex (γ-TuC), a large multi-protein complex enriched at microtubule organising centres such as the centrosome. Many aspects of γ-TuC regulation remain a mystery. We discovered the fission yeast proteins Mto1 and Mto2, which form an oligomeric complex (the Mto1/2 complex). Mutations in the human homolog of Mto1 lead to the brain disease microcephaly. We have shown how Mto1/2 targets the γ-TuC to different sites in the cell and we have also shown that also Mto1/2 activates the γ-TuC in vivo. We have reconstituted microtubule nucleation in vitro using purified γ-TuC and Mto1/2 proteins, and we have characterised Mto1/2 through cross-linking mass spectrometry and X-ray crystallography. Our current work is focused on understanding how Mto1/2 complex activates the γ-TuC.

As part of our work, we develop new tools in genetics, microscopy, and proteomics as needed. These have included a robust platform for differential proteomics in fission yeast, engineering of signalling pathways in vivo, and new methods for interrogating protein-protein interactions in complex “solid-phase” organelles.

See what we’ve published


Current funders of our work.